1. Field of the Invention
The present invention relates generally to a switch configuration for key-entry operation and, more particularly, to a key-entry switch device (hereinafter referred to as a key switch) preferably used for a keyboard incorporated, as an input device, in electronic equipment. The present invention also relates to a keyboard provided with a plurality of key switches. The present invention further relates to an assembling jig usable for assembling a key switch.
2. Description of the Related Art
In a thinner or low-profile-type keyboard for a portable electronic apparatus, such as a notebook or palm-top personal computer, it is required to reduce the height of a key switch for a key-entry operation as well as to improve the operability of the key switch. The key switch usable in the low-profile keyboard generally includes a support plate (e.g., a metal sheet, a bottom panel of a keyboard, etc.), a key top arranged above the support plate, a pair of link members interlocked to each other to support the key top above the support plate and direct the key top in a vertical or up-and-down direction, and a switch mechanism capable of opening and closing a contact section of an electronic circuit in accordance with the vertical or up-and-down movement of the key top. The key top is movable substantially in the vertical direction relative to the support plate, through an interlocking action of the link members, while keeping a predetermined posture of the key top. Key-entry operability of the key switch is affected by the amount of stroke (the vertical movement) of the key top and by key-entry operation properties accompanying a so-called “click feeling” during the vertical movement.
Conventionally, in the above key switch, several types of link-member pairs have been used. For example, the first type of link members, which may be referred to as a gear-link type, are assembled together into a reverse V-shape as seen in a lateral direction (or in a side view) and meshed at toothed end regions thereof with each other (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 2003-031067 (JP-A-2003-031067)). The second type of link members, which may be referred to as a pantograph type, are assembled together into an X-shape as seen in a lateral direction (or in a side view) and are rotatably or slidably joined at the intersections thereof with each other (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 2002-231090 (JP-A-2002-231090)). Also, a widely-used switching mechanism is configured from the combination of a sheet-like switch including a pair of flexible circuit boards respectively carrying contacts in a mutually facing arrangement (referred to as a membrane switch sheet, in this application), and an actuating member disposed between the key top and the membrane switch sheet and acting in accordance with the downward motion of the key top to close the contacts.
In a key switch disclosed in JP-A-2003-031067, a base panel shaped as a flat frame is disposed on a membrane switch sheet spread and placed on a support plate. Each of a pair of link members combined in the reverse V-shape as seen in a side view is provided at one end thereof with one or more teeth constituting a meshing structure and a pivoting part pivotally joined to the key top, and at another end opposite thereto with a sliding part slidably engaged with a guide section formed in the base panel. During the period when the key top moves in the vertical direction, the link members pivot about the pivoting part in a mutually interlocking manner through the meshing structure, and the respective sliding parts slide along the upper surface of the membrane switch sheet under the guidance of the guide section of the base panel. A dome-shaped actuating member formed of a rubber is used in the switch mechanism. The actuating member is fixed to the membrane switch sheet in the opening of the base panel, with a dome-top thereof facing toward the key top. On the inner surface of the dome-top of the actuating member, a protrusion is formed to be aligned with the contact section of the membrane switch sheet, which acts to press and close the contact section as the key top is lowered. In this key switch, a click feeling in a key-entry operation is ensured by the buckling or elastic deformation of the rubber-made dome-shaped actuating member.
In a key switch disclosed in JP-A-2002-231090, a through-hole is formed in the membrane switch sheet spread and placed on the support plate, so that a guide section and a pivot-support section, provided on the support plate, extend through the through-hole to project from the membrane switch sheet. In the pair of link members combined in the X-shape in a side view, one link member is provided at one end thereof with a pivoting part joined pivotally to the key top and at another end with a sliding part slidably engaged with the guide section of the support plate, while the other link member is provided at one end thereof with a pivoting part pivotally joined to the pivot-support section of the support plate and at another end with a sliding part slidably engaged with the key top. During the period when the key top moves in the vertical direction, the link members pivot in a mutually interlocking manner through a generally center pivoting structure, and the respective sliding parts slide along the key top and the support plate. The link members are also connected together through a return spring shaped in a plate spring, and a plate-spring shaped actuating member separated from the return spring extends from one link member. At the end of the actuating member, a protrusion is formed to be aligned with the contact section of the membrane switch sheet, which acts to press and close the contact section as the key top is lowered. In this key switch, a click feeling in a key-entry operation is ensured by the buckling or elastic deformation of the return spring.
Incidentally, it has been known that a keyboard including a plurality of key switches is configured in such a manner that, in order to improve a key-entry operability of the key tops disposed in a predetermined array on the upper surface of the keyboard housing and to thereby reduce fatigue of an operator, an operator can put his both hands on the keyboard in a natural position where the finger tips of both hands generally converge toward each other and, while maintaining this natural position, can perform a key-entry operation by his finger tips on the top surfaces (i.e., key-operating surfaces) of the respective key tops (see, e.g., Unexamined Japanese Patent Publication (Kokai) No. 8-234882 (JP-A-8-234882)) without sensing any incongruity. The keyboard disclosed in JP-A-8-234882 has a configuration wherein the normal parallel arrangement of the plural key switches is maintained, and wherein the key-operating surfaces of the respective key tops are formed so as to show, in a right-hand key switch group as seen from the operator, a rectangular profile with the right end thereof descending in a plan view, and to shown, in a left-hand key switch group as seen from the operator, a rectangular profile with the left end thereof descending in a plan view. With this configuration, it is possible to prevent the increase in dimension (or occupying area) of the keyboard, in comparison with a configuration in which the respective key switches are arranged obliquely to conform to the natural converging postures of the hands.
The key switch disclosed in JP-A-2003-031067 is configured such that, in the key-entry operation, the gear-link type pair of link members slides at the respective sliding parts along the upper surface of the membrane switch sheet. Therefore, the thicknesses of the support plate and the membrane switch sheet are included in the dimension in the height direction of the key switch. Also, at an instant when the key top reaches the lowermost position of the vertical movement, the link members are disposed to be substantially in contact with the upper surface of the membrane switch sheet at regions between the sliding and pivoting parts thereof, which determines the amount of stroke of the vertical movement. Thus, it is necessary to reduce the thickness of the membrane switch sheet, in countermeasures for height reduction and operability improvement of the key switch. In practice, however, it is considered that the thickness of the membrane switch sheet has been reduced to a physical limit.
In contrast, the key switch disclosed in JP-A-2002-231090 is configured such that, in the key-entry operation, the sliding part of one link member of the pantograph type pair of link members slides, inside the through-hole of the membrane switch sheet, along the guide section of the support plate. Therefore, it is possible to eliminate the influence of the thickness of the membrane switch sheet on the height dimension of the key switch. Also, at an instant when the key top reaches the lowermost position of the vertical movement, the link members are received inside the through-hole of the membrane switch sheet at regions between the sliding and pivoting parts thereof. Therefore, it is also possible to eliminate the influence of thickness of the membrane switch sheet on the amount of stroke of the vertical movement of the key top. Contrary to this, the support plate is also provided with a through-hole at a location corresponding to the through-hole of the membrane switch sheet, so that the link members are supported on the support plate, during the key-entry operation, by only the guide section and the pivot-support section provided locally in the support plate. As a result, the stability of the interlocking movement of the link members (especially, of the sliding motion of the sliding part) may be degraded, and thus the key-entry operability of the key top may be impaired.
On the other hand, in the keyboard disclosed in JP-A-8-234882, the plural key switches are arranged such that the profiles of the key-operating surfaces of the key tops in the right-hand group are generally symmetrical to those in the left-hand group as seen from the operator. Therefore, in order to operate the key switches without sensing incongruity at the finger tips, the operator is required to use both hands in correspondence with the positions of the key switches. This configuration may be difficult, especially for an inexperienced operator. Further, the plural key tops having substantially same size and different shape are used in the above keyboard, so that the assembling process of the keyboard may become complicated and thus may lead to increase in the manufacturing cost.
Further, as the height reduction of the key switch is facilitated, the dimensions, especially of the link members, is decreased. Also, the assembling process of the key switch has often been performed manually, and it becomes difficult to manually assemble the small-sized link members accurately on the support plate, without causing damage or loss of the link members. Thus, it has been required to develop an assembling jig usable in the process for assembling the low-profile key switch.